One of the funniest things I ever saw was ventriloquist Jay Johnson and Darwin on "The Tonight Show with Johnny Carson." Must have been about 1985 or '86, because I can remember my college roommate and I just laughing hysterically at the routine.
THIS CLIP is from a fairly recent Letterman show, but it's similar to the Carson stint and very, very funny.
For more laughs, check out THIS RIFF on Janet Jackson from the gals at Go Fug Yourself. Classic!